1. Field of the Invention
This invention relates generally to the field of petroleum production and fluid separation. In particular, the invention relates to a novel technique for driving components of a submergible pumping system including an oil/water separator for separating production fluids from non-production fluids in a wellbore.
2. Description of the Related Art
Various techniques have been devised for raising production fluids from petroleum wells. In general, where a well has sufficient pressure to raise fluids without assistance, the well may be exploited directly by the control of above-ground valving and other equipment. In many wells, however, production fluids must be raised to the earth's surface by artificial means, such as submergible pumping units. Known submergible pumping systems typically include a submergible electric motor coupled to a submergible pump. The electric motor is coupled to power supply and control circuitry at the earth's surface, and is energized to drive the pump. The pump and motor unit is submerged in the wellbore fluids. The pump transfers fluids from the wellbore to the earth's surface via a discharge conduit.
In an increasing number of wells, fluids entering the wellbore comprise a mixture of both production and non-production fluids, typically crude oil and water or brine. The non-production fluids must therefore be separated from production fluids either prior to or following extraction of the production fluids from the well. While the non-production fluids can be raised to the earth's surface and subsequently separated from the production fluids, removed water must then be disposed of, such as by reinjection into a disposal well. Moreover, production from the well is typically limited by the capacity of the pumping system, and by the amount of power input to the pumping system. Consequently, it is often more advantageous to separate non-production fluids from production fluids in the wellbore and to raise only the production fluids from the well. Non-production fluids such as water may then be directly reinjected into a subterranean disposal or injection zone.
Several techniques have been proposed and are currently in use for separating production fluids from non-production fluids in a wellbore. In some wells, the fluids may be separated by gravity, and submergible pumps used to raise production fluids and to reinject non-production fluids. Often, however, it is desirable to employ artificial separating means, such as mechanical separators. In one known type of separator, commonly referred to as a hydrocyclone separator, mixed production and non-production fluids are circulated through a separator vessel. Rotational velocity of the fluid causes different fluids having different specific gravities to separate from one another radially. The fluids, including production fluids and aqueous components, are removed from the separator in a continuous flow. Production fluids are then transferred to a production pump from which they are conveyed to the earth's surface for collection. Non-production fluids may be injected into a discharge horizon either by a separate pump, or currently, directly from the separator.
Such hydrocyclone separators offer a number of advantages over other separation techniques. In particular, hydrocyclone separators, which may be thought of as passive devices, have no moving parts, and may be used in groups to increase the throughput capacity of the system. While only coarse separation is typically attained through hydrocyclone separators, the ability to obtain relatively continuous separation in situ provides an attractive option to raising non-production fluids for subsequent separation and disposal.
Other in situ separators are also known which permit similar separation of production and non-production fluids within a wellbore. Such devices, which may be thought of as active separators, include centrifugal separators which mechanically impart rotational forces on the mixed fluids to separate production and non-production components from one another.
Known downhole separation configurations are, however, not without drawbacks. For example, depending upon the relative locations of production zones, discharge or injection zones, production rates and reject ratios (i.e., the portion of the wellbore fluids to be discharged or reinjected into designated formations), proper plumbing between pumps in a pumping system may be difficult or impossible. In general, hydrocyclone separators have been positioned at the end of a pumping system and supplied with unseparated wellbore fluids via a first pump. Because a second production pump is often physically distant from the separator in the pumping system, production fluids from the separator must then be routed via transfer tubing to the production pump for transfer to the earth's surface. However, where production and injection zones must be isolated from one another by means of packers or similar devices, routing fluids between the first pump and the separator, and between the separator and the production pump is complicated by the need to traverse the packers. Moreover, in many situations there may be insufficient clearance between the pumping system and the wellbore casing to permit passage of the needed transfer tubing between the components.
There is a need, therefore, for an improved technique for separating fluids in a wellbore that avoids such drawbacks of prior art systems. In particular, there is a need for a fluid separating system that affords a greater degree of freedom in the order of assembly and placement of pumping system components, including drive motors, injection and production pumps, separators, and so forth, facilitating piping between the components in the various configurations.